BRUSSELS (Reuters) - NATO does not expect to base nuclear weapons or large numbers of new combat troops in eastern Europe, despite tension with Russia over Ukraine, Secretary-General Anders Fogh Rasmussen said on Monday.

NATO officials also said Russian and NATO ambassadors may meet as early as next week to discuss the Ukraine crisis.

In 1997, during a period of better relations, NATO reached an agreement with Russia under which alliance members said they had no intention of deploying nuclear weapons on the territory of new member states, which began joining in 1999 after the collapse of the Soviet Union.

Under that agreement, NATO also committed to defending its members through reinforcement rather than by permanently stationing additional "substantial combat forces" on their territory.

Asked if the Ukraine crisis would lead NATO to reconsider its pledge not to place nuclear weapons on the territory of new member states, Rasmussen told a news conference: "At this stage, I do not foresee any NATO request to change the content of the NATO-Russia founding act (the 1997 agreement)."

He said, however, that Russia's actions in Ukraine had created "a completely new security situation in Europe" and NATO must adapt accordingly. Long-term decisions would be taken when NATO leaders meet in Wales in September, he said.

Since Russia annexed Ukraine's Crimea, NATO has moved to reassure its nervous eastern European. Ships and planes have been temporarily deployed to their countries and military exercises in the region stepped up.

Poland has urged NATO to base troops on its territory permanently, something Russia says would break the 1997 agreement.

Some NATO diplomats argue privately that, by annexing Crimea, Russia has broken the 1997 agreement, under which Russia and NATO pledged not to threaten force against any state.

Rasmussen also said that NATO had proposed a meeting of Russian and NATO ambassadors, possibly next week, but had not yet heard back from Moscow.

A NATO official said Russia had indicated it wanted to discuss the Ukraine crisis with NATO and just the date remained to be set.

NATO last month suspended all practical cooperation with Russia to protest the annexation of Crimea. It left open the possibility of high-level dialogue.